This invention relates generally to television channel selection, and more particularly relates to the keyboard selection of a television channel and the microcomputer-controlled display of and tuning to the selected channel number.
Television receivers are generally tuned by rotating a tuning knob to sweep the broadcast frequency band which has been preselected by means of a frequency band switch. The currently tuned channel indication is provided by the channel number indicator which moves along a scale. This type of television tuning system utilizes mechanical and electromechanical components and is characteristically slow in response, noisy, subject to mechanical breakdown and best suited for use with a limited number of channels. The proliferation of UHF channels and the increasing use of CATV and MATV have rendered these electromechanical tuning systems of limited utility in current television receivers. The all-electronic, all-channel tuning system has thus been developed to meet current television tuning system demands. Electronic tuning systems are characterized by silent operation, high speed, all-channel tuning and solid state electronics reliability. In these systems, channel selection is typically by means of a 10-digit, push button keyboard entry with channels accessed either substantially in a stepwise manner or by direct channel tuning. While these digital electronic tuning systems permit extremely rapid channel selection, no allowance is made for user entries which are erroneous in terms of the channel desired and that which was actually selected or which involve the entry of an illegal (non-FCC designated) channel number.
The prior art includes several approaches to optimizing the user-tuner interface by reducing the possibility of erroneous tuner inputs and ameliorating the resulting inconvenience. U.S. Pat. Nos. 3,931,579 to Ma et al and 3,980,958 to Tanaka illustrate one approach for compensating for an illegal channel number entry wherein signal recognition means cause the channel number selection means to sequence to another number if no television signal is received. This technique utilizes a comparator to compare the information from the channel number selection means with the information from a local oscillator to determine the presence of an acceptable signal within a restricted range about the frequency corresponding to the designated channel number. The comparator is coupled to a ramp voltage source for controlling both the tuning voltage direction and rate of change in making corrections to the local oscillator frequency in tuning to the desired channel. After a predetermined delay, information from the comparator is analyzed for coincidence with a signal from the recognition means in a channel selection control and if signal coincidence is lacking the channel counter sequences to the next designated channel number. This approach thus permits an illegal channel number and any unused channel to be quickly bypassed in a sequential fashion but does not allow for either user verification of the selected channel number prior to channel switching following channel number entry or return to the previously tuned channel following an erroneous or illegal channel number entry.
Another approach is disclosed in U.S. Pat. No. 3,973,228 to Mueller et al involving the automatic sequential stepping from channel to channel at a first relatively slow rate for preselected channels to which the receiver is to respond and for skipping over other non-selected channels at a relatively high frequency. This permits the rapid detection and rejection of a selected illegal channel but also involves the inconvenience of sequencing through all channels intermediate between an illegal channel and the original channel to obtain the channel which was originally tuned in. In addition, the erroneous selection of a legal channel also necessitates the sequential stepping through of intermediate channels before regaining the original channel.
Still another approach to the problem of erroneous channel selection is disclosed in U.S. Pat. No. 4,162,513. The microcomputer-controlled electronic tuning system as described therein provides for the entry of an illegal channel number by causing the tuner not to respond to such an entry and the channel number display to remain unchanged. However, this procedure is complicated by the fact that some illegal channel numbers are used to select various modes of selector operation, e.g., illegal channel number 00 is used to turn the receiver off, and because the device itself is designed primarily as a channel programmer for automatically tuning in a selected channel at a future predetermined time. In addition, this system fails to provide for the temporary display of the erroneously selected channel number to permit user correction of an erroneous entry prior to receiver tuning to the unwanted channel. A more remotely related channel number entry approach involving the use of a microcomputer is disclosed in "A Microcomputer Controlled Frequency Synthesizer for TV," IEEE Transactions on Consumer Electronics, Vol. CE-24, No. 2, May 1978, by Rzeszewski et al.
In accordance with the present invention, the aforementioned channel selection problems are eliminated by means of a two-step channel selection process--channel number entry followed by a second entry withn a predetermined time period.